Sound created in an enclosed space will interact with the surfaces and objects of the space, and will convey to the listener not only particulars of the sound source, but also a sense of the architecture and materials present in the space—for instance, consider the sounds in a small wood-frame church compared to those in a racquetball court. As a result, artificial reverberation is widely used in music and film production to place sounds in an architectural context or produce a desired “feel.”' Furthermore, the acoustics of the space help convey the positions of the source and listener within the space. Recording engineers will carefully place microphones in a room to adjust the timbre and spatial balance of the recording, and film audio engineers will separately manipulate wet and dry versions of a sound source according to its position in an attempt to simulate motion of the source or listener within a space.
Commercially available digital reverberators are typically implemented using either delay line networks or convolution (see, e.g. V. Valimaki et al., “Fifty Years of Artificial Reverberation,” IEEE Transactions on Audio, Speech, and Language Processing, vol. 20, no. 5, pp. 1421-1448, July, 2012 (“Valimaki”)). Convolutional reverberators imprint audio with a desired room impulse response, using frequency domain methods for computational efficiency, while dividing the impulse response into segments to minimize computational latency (see, e.g., W. G. Gardner, “Efficient Convolution without Input-Output Delay,” J. Audio Eng. Soc., vol. 43, no. 3, pp. 127-136, 1995; D. S. McGrath, “Method and apparatus for filtering an electronic environment with improved accuracy and efficiency and short flow-through delay,” U.S. Pat. No. 5,502,747, Mar. 26, 1996; and G. Garcia, “Optimal Filter Partition for Efficient Convolution with Short Input/Output Delay,” Audio Engineering Society Convention 113, October, 2002). These methods may be able to faithfully reproduce the desired room impulse response, but are difficult to interactively control, and can be computationally expensive, requiring memory and computation roughly in proportion to the room impulse response length. The indexing required by the FFT and sample memory needed make on-chip implementation difficult.
Networks of delay lines and filters can be configured to produce responses that are perceptually similar to those of room reverberation, with a set of early reflections giving way to a dense late field reverberation (see, e.g. Valimaki). Using such structures, gross reverberation features, e.g., the late field reverberation equalization and decay times, may be interactively adjusted, but details of the timbre are difficult to control. Schroeder-type (e.g. M. R. Schroeder, “Natural Sounding Artificial Reverberation,” Audio Engineering Society Convention 13, October, 1961) and feedback delay network (e.g. J. M. Jot, “Digital Delay Networks for Designing Artificial Reverberators,” in Audio Engineering Society Convention 90, February, 1991) structures are widely used and efficient computationally, though they require on the order of one or two seconds of memory to produce high-quality reverberation.
Thus there is a need for an artificial reverberator that both can faithfully reproduce a given acoustic space and can be interactively controlled. There is also a need for artificial reverberation methods which require little memory. Additionally, there is a need for an artificial reverberator which allows movement of a source and/or listener within an acoustic space. Similarly, there is a need for an artificial reverberation method which efficiently processes multiple sources or listeners.